The Collaborative International Dictionary of English v.0.48:

Contractor \Con*tract"or\, n. [L.]
   One who contracts; one of the parties to a bargain; one who
   covenants to do anything for another; specifically, one who
   contracts to perform work on a rather large scale, at a
   certain price or rate, as in building houses or making a
   railroad.
   [1913 Webster]

WordNet (r) 3.0 (2006):

contractor
    n 1: someone (a person or firm) who contracts to build things
    2: the bridge player in contract bridge who wins the bidding and
       can declare which suit is to be trumps [syn: contractor,
       declarer]
    3: (law) a party to a contract
    4: a bodily organ that contracts [syn: contractile organ,
       contractor]